What I know is that the process is sped up by turning up the throttle and using afterburners. I know fuel isn't the cause, because there is still fuel when it turns off. Also all the instruments and electrical elements fail, so i think this may be the cause. What do I do?

The Concorde has many tanks that all go into four tanks -- one per engine using various valves IIRC.So if you don't manage it appropriately, then you will either stall with imbalance problems (my usual problem ) or run out of fuel. Problem is I never learned how to use the Concorde properly

You need manage fuel.There are many fuel tanks, in basicaly, after take off switch on pumps on tanks 5, 7, 6 and 8, that pumps will feed main fuel tanks 1 - 4 with fuel. Tanks 9,10 and 11 are used for trim. Without proper trimming You never reach FL500 and Mach 2. For more information check http://wiki.flightgear.org/Concorde#Fuel_Management.